A power factor corrector or a power factor correction circuit (PFC) is a front-end power stage of a grid-connected power converter, such as a power supply, motor drive and electronic ballast [1] to [3]. It is used to meet international grid current standards, such as IEEE519 and IEC-61000-3-12. These standards are also applied to a single-phase grid network which can be used as an AC power source for low power industrial applications and household devices. Using a PFC in a system ensures a sinusoidal input current and a stable output DC voltage. It can also be foreseen that the PFC will be a very important device to ensure a good power quality in a more complex grid network.
In a known PFC, a diode bridge and a boost converter are used. The diode bridge rectifies the grid current and voltage. The boost converter shapes inductor current into rectified sinusoidal current. As a result, grid current is sinusoidal and in-phase of grid voltage. This converter is simple and low-cost, since only one active switch is in the circuit. Thus, it is popularly adopted by lighting applications. However, the drawback of the circuit is a high conduction loss for high power applications since there are three semiconductors in the current path, irrespective of whether the controlled switch is on or off. Moreover, a large high frequency filter is used due to a large peak-to-peak high frequency ripple current carrying on the gird current.
In order to solve the conduction loss issue of the known PFC, a bridgeless PFC is proposed in [4]. The PFC integrates a diode bridge and a boost converter into one power stage, including two switching arms. One switching arm shapes half line cycle grid current. Two grid inductors are always in series, irrespective of the switching state. The circuit gives a low conductional loss, since it has only two semiconductors in the current paths. However, it is more expensive because of the more active device and magnetic components. In addition, there is a grounding problem, or a common mode voltage or leakage current issue, when it is operating. In addition, a high frequency filter is still included.
Some modifications of bridgeless PFC circuits have been proposed to tackle the issue of leakage current. A bridgeless PFC with a series semiconductor switch is presented in [5]. The series switch is synchronized with a main switching for current shaping. Thus, grid terminals are electrically isolated during inductor current charging states. Then, a low leakage current can be generated. However, it involves one higher-rated voltage, higher-rated current and higher switching frequency semiconductor switch in the main current flowing path. As a result, the conduction loss is higher than the simple bridgeless PFC during inductor current discharging states. The fundamental idea of the bridgeless PFC is distorted and it is expensive. In addition, a high frequency filter is still included.
Another method of eliminating the common mode voltage issue is to use a bi-directional switch to charge up an input inductor current [6]. When the bi-directional switch is closed, all diodes are off due to a reverse bias by the output dc voltage. This leads to electrical isolation during that switching stage.
There are thus always two semiconductors in the current paths. However, as the diode bridge is switching at a high frequency, four expensive fast diodes are used. The conduction performance of a fast diode is often not as good as that of line frequency diodes. A floating gate drive is another cost issue for this topology. In addition, a high frequency filter is still included.
A diode clamped bridgeless PFC is proposed in [7]. It provides a simple and efficient solution for tackling the common mode voltage issue. In this bridgeless PFC, two diodes connect the circuit ground to a positive terminal and a negative terminal of the AC power source, respectively. These two line frequency diodes guarantee that no common mode voltage difference occurs between the ground and the AC source. However, grid inductors work in half line cycle only, which means that two separate and identical inductors are used. The high cost and large size of the inductors are problematic. In addition, a high frequency filter is still included.
To address the use of expensive magnetic devices, a single core inductor is introduced in [8]. By this method, the size issue can be solved due to the use of one magnetic core. However, the design of the inductor is very difficult. In addition, a high frequency filter is still included.
Instead of diodes, capacitors can be used to maintain the voltage difference between the ground and the AC power sources. A capacitor clamped bridgeless PFC is disclosed in [9]. The capacitors are coupled to the grid terminals and the ground, whereby a low leakage current can be ensured, but a high frequency current ripple can still be found at the grid current; thus, a high frequency filter is still included.
A built-in common filter is disclosed in [10]. In this modification, a common mode filter connects serially with boost chokes, two capacitors perform functions of voltage clamping and filtering. The topology effectively reduces leakage current, but it does not help in filtering out the high frequency components from the grid current.
An improved capacitor clamped approach is proposed in [11]. In this design, two switches are used to connect the voltage clamped capacitors. According to the disclosure, the additional switches are switching at the same time and the switches are used to improve the efficiency during light load operation. Thus, it can be estimated that the performance should be more or less the same as that of a simple capacitor clamped bridgeless PFC.
The known solutions can effectively solve the common mode voltage issue of the bridgeless PFC, but the penalties include a higher conduction loss and more or larger passive devices. Moreover, not all solutions can improve the grid current quality.